When electron get sufficient energy and become unstable and to stabilized again it emit energy in form of radiation

The emission spectrum of a material results from the transition of its atoms or molecules from an excited state to a lower energy state. This transition occurs when the material absorbs energy, typically in the form of photons, and then releases that energy in the form of electromagnetic radiation. The emitted radiation has a characteristic spectrum that depends on the specific energy levels of the material.

Transition from excited to normal state:
The correct answer is option D, which states that the emission spectrum results from the transition from an excited state to a normal state. When atoms or molecules are in their normal or ground state, their electrons occupy the lowest energy levels. However, when they absorb energy, such as through heat or light, the electrons become excited and move to higher energy levels. These excited states are not stable, and the electrons eventually return to their normal state by releasing the absorbed energy.

Key points:
- Transition from excited to normal state refers to the process of electrons returning from higher energy levels to their ground state.
- This transition results in the emission of photons with specific wavelengths.
- Each electron transition corresponds to a specific amount of energy being released, which determines the wavelength or color of the emitted light.
- The emission spectrum of a material is a unique pattern of wavelengths or colors that are emitted when the material is excited and then returns to its ground state.
- The emission spectrum can be observed as distinct lines or bands of colors when the emitted light is passed through a prism or spectrograph.

In summary, the emission spectrum of a material is the result of the transition of its atoms or molecules from an excited state to a normal state. This transition involves the release of energy in the form of electromagnetic radiation, which produces a characteristic spectrum of wavelengths or colors.